1. Field of the Invention
The present invention relates to a roll-resistant hydraulic suspension system for a load handling vehicle.
2. Description of Related Art
In recent years, large load carrying vehicles, such as ore carriers, have become even larger so that they carry increasingly heavy loads. At the same time, such vehicles have become equipped with larger engines, giving the vehicles the capacity to operate at relatively high speeds. These greater loads and higher speeds have accentuated a shock-dampening problem. In particular, it has been found that such vehicles when heavily loaded and operated at high speeds on rough terrain, have a tendency to roll or tilt to one side, especially in turns.
More specifically, FIGS. 1-7 and 10 depict schematically a conventional heavy load carrying vehicle 10, such as an articulated underground mining vehicle for carrying heavy ore loads, for which the present invention is intended to be used. As best shown in FIG. 1, the vehicle includes a front vehicle or tractor portion 10a, and a rear load-carrying portion 10b interconnected at a steerable vertical hinge axis 11.
Front vehicle portion 10a includes a pair of wheels 12a, 12b (FIG. 3) mounted at the opposite ends of an axle 14 carried by a generally V-shaped subframe 16. Subframe 16 is connected to the main vehicle chassis 17 (see FIGS. 3-7) at a spherical bearing 18 such that the subframe 16 is effectively cantilevered forward from and beneath chassis 17. A pair of hydraulic suspension cylinders 26a, 26b interconnect the free ends of the subframe 16 and main chassis 17 to isolate the chassis from shock loads transmitted to the subframe from the ground and to control the height of the chassis 17 above the subframe. By adjusting the hydraulic pressure and/or volume at the top ends of cylinders 26a and 26b, the height of the chassis 17 above the subframe 16 can be adjusted. Such height adjustments are numerous during operation of the vehicle because of the large weight difference between a loaded and unloaded vehicle and the need to maintain appropriate clearance between the subframe 16 and chassis 17 during all phases of loading and unloading of the vehicle.
Because of the spherical bearing-mounting of subframe 16 relative to chassis 17, the subframel6, as viewed in elevation (FIG. 5), can pivot vertically in the directions of arrow 20 about spherical bearing 18. Similarly, as viewed from the front, as shown in FIGS. 6 and 7, any force encountered by one wheel, such as wheel 12a traveling over a rock, urges that wheel upwardly relative to the chassis, causing axle 14 to pivot in the directions of arrows 22 about the longitudinal axis 19 of the vehicle through spherical bearing 18, thus urging opposite wheel 12b downwardly relative to the chassis about the same axis. Suspension cylinders 26a and 26b when hydraulically-coupled to accumulators 28a, 28b are intended to dampen such vertical movements of the axle and subframe caused by the vehicle traveling over rough, uneven terrain.
One known hydraulic circuit 39 for such suspension systems is shown schematically in FIG. 10. The pressure sides of both hydraulic cylinders 26a, 26b are continuously hydraulically interconnected and share common pressure from accumulators 28a, 28b though hydraulic lines 43. Similarly, the exhaust sides of both cylinders are hydraulically interconnected through hydraulic lines 45. The system also includes a pressure bleed down valve 60 for de-pressurizing the system for maintenance.
A suspension height sensor 25 (see FIGS. 8 and 9) commands the leveling valve 46. When height sensor 25 senses that the height of the vehicle's chassis relative to its subframe is at an optimal height, leveling valve 46 is spring-centered in its neutral position shown in FIG. 10 to isolate the hydraulic lines 43 from pressure source 54, thereby maintaining the same pressure and volume in the pressure sides of both hydraulic cylinders 26a, 26b to maintain the optimal height.
Should the sensed height of the vehicle be too high, the leveling valve 46 is mechanically-commanded to the left in FIG. 10 to a position that connects hydraulic lines 43 with storage tank 56, thereby allowing fluid in lines 43 to vent to the tank 56 and reducing pressure at the top ends of both cylinders and in accumulators 28a, 28b to lower the chassis relative to the subframe until the chassis is at the desired height as sensed by the height sensor 25, at which point valve 46 returns to its spring-centered neutral position.
Should the sensed height of the vehicle be too low, the leveling valve 46 is mechanically-commanded to the right in FIG. 10 to a position that connects hydraulic lines 43 with a hydraulic pressure source 54, allowing hydraulic fluid under pressure to be transmitted thorough hydraulic lines 43 to the top ends of both cylinders 26a, 26b and to the accumulators 28a, 28b. This causes the cylinders to extend to raise the chassis to the desired level as sensed by the height sensor 25, at which position leveling valve 46 returns to its spring-centered neutral position. Thus, although pressure in the hydraulic cylinders and accumulators, and thus the height of the chassis, can be modulated with the existing circuit, the hydraulic cylinders 26a, 26b and the respective accumulators 28a, 28b remain hydraulically interconnected during normal operation of the vehicle.
To illustrate, when a heavily loaded such vehicle turns at high speed, or when one wheel hits a bump, the force generated has a tendency to cause the chassis to roll or tilt to one side relative to the axle and subframe (see FIG. 7). With a conventional hydraulic circuit for the suspension system, this tendency to roll is accentuated because the pressure sides of both suspension cylinders are hydraulically interconnected and share a common source of pressure fluid, such as accumulators 28a, 28b. Similarly, the exhaust sides of both cylinders are interconnected. Thus, for example and as shown in FIG. 7, when chassis 17 begins to roll to the right (or the right wheel 12b moves upward relative to the chassis) as shown, it tends to retract cylinder 26b, displacing fluid from the pressure side of that cylinder 26b. This displaced fluid is transmitted to the pressure or top side of the other suspension cylinder 26b, which tends to extend that cylinder as shown, and thereby accentuating the tendency of the chassis to roll to the right.
U.S. Pat. No. 5,443,283 to Hawkins discloses an independent swing arm suspension with one leveling valve for each wheel. In the Hawkins suspension, each wheel is independently suspended at all times and requires its own leveling valve. Thus, the two cylinders corresponding to each of an opposing pair of wheels can not be operated together to adjust the height of the vehicle uniformly.
U.S. Pat. No. 4,971,353 to Buma, U.S. Pat. No. 4,593,931 to Shiratori, and U.S. Pat. No. 5,642,282 disclose various independent suspension systems. U.S. Pat. No. 2,964,333 discloses a conventional leveling valve construction.
None of these prior systems reflects an appreciation of the roll problem. The suspension system having a hydraulic circuit according to the present invention, described below with reference to FIGS. 8, 9, and 11-13 overcomes this problem by resisting the tendency of the chassis to roll relative to the subframe.